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Rpms Jumping


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Okay I have a 99 Cummins auto 4x4 with 199,000 on it and I just replaced the ecm and pcm and everything worked great till yesterday when I picked it up from having the u joints and axle seals done now it doesn't like to shift into that deep drone overdrive, if I accelerate lightly after 4th gear it will jump rpms then go into overdrive. It will sometimes jump rpms in other gears depending on what certain speed I am at. So what is the issue? I have heard alternator, tps sensor or crank sensor. This issue gets worse as I drive it to where it will jump in all gears no matter what speed till I pull over and poke around then it wont do it as bad for a little bit.
 

 

 

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Why pcm/ecm?  If they just died, I bet your alternator or another electronic surge is killing them. 

You need to find the issue before you drive the truck if it is electrical. 

A multimeter on ac mode should see less than 0.1VAC.

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Can you go into more detail on how it shifts and when it jumps?

 

The 47re is a 4 speed trans so I am confused by your post. 

Shifting goes, 1, 2nd,3rd, 3rd with tc lockup, 4th, 4th with tc lockup.

 

3rd lockup happens around 35 mph, 4th should happen 45 mph or right after the 3-4 shift.

 

If it is jumping after you hit 4th then the truck is jumping in and out of lockup.  

 

How rapid is the junping? x times a second?

If it is very rapid then I would say your tc is getting bad, if it is slower I would say your at is causing ac noise which is causing lockup to jump.

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  • 10 months later...

Hello, I have a similar condition. 1999 1 ton auto trans. It likes to gear hunt between 1200 and 1500 rpm. if I turn overdrive off rpms increase to +/- 2000 and the gear hunting ceases. This occurs right at about 45-50 mph. similarly if overdrive is off the same happens at lower speeds 25-30ish, same rpm range though. A friend suggested a vacuum leak, or possibly solenoids, TC lockup. This only happens when trying to maintain a constant speed, if actively accelerating the hunting doesn't take place. Thanks for reading, and any suggestions.

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